U.S. patent application number 15/230314 was filed with the patent office on 2017-02-09 for catheter with inductive force sensing elements.
The applicant listed for this patent is Boston Scientific Scimed Inc.. Invention is credited to John C. Potosky, Darrell L. Rankin.
Application Number | 20170035357 15/230314 |
Document ID | / |
Family ID | 56877114 |
Filed Date | 2017-02-09 |
United States Patent
Application |
20170035357 |
Kind Code |
A1 |
Rankin; Darrell L. ; et
al. |
February 9, 2017 |
CATHETER WITH INDUCTIVE FORCE SENSING ELEMENTS
Abstract
Various embodiments concerns a system for measuring a force
within a body comprising a catheter, the catheter comprising at
least one sensor and an element located within the catheter, the
element displaceable within the catheter relative to the at least
one sensor. The system further comprises control circuitry
configured to measure, for each of the at least one sensor, a
change in a resonance frequency of the sensor based on a change in
distance between the sensor and the element, the change in distance
responsive to the force. The control circuitry is further
configured to calculate at least one parameter of the force based
on the change in the resonance frequency, and output an indication
of the at least one parameter of the force.
Inventors: |
Rankin; Darrell L.;
(Milpitas, CA) ; Potosky; John C.; (San Jose,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Boston Scientific Scimed Inc. |
Maple Grove |
MN |
US |
|
|
Family ID: |
56877114 |
Appl. No.: |
15/230314 |
Filed: |
August 5, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62202324 |
Aug 7, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/742 20130101;
A61B 2562/04 20130101; A61B 5/02 20130101; A61B 5/6852 20130101;
A61B 2018/00773 20130101; A61B 5/6885 20130101; A61B 2018/00577
20130101; A61B 2018/00642 20130101; A61B 18/1492 20130101; A61B
2018/00351 20130101; A61B 2018/00988 20130101; A61B 2090/065
20160201 |
International
Class: |
A61B 5/00 20060101
A61B005/00; A61B 18/14 20060101 A61B018/14; A61B 5/02 20060101
A61B005/02 |
Claims
1. A system for measuring a force within a body, the system
comprising: a catheter comprising at least one LC circuit and at
least one mass of high magnetic permeability material, each LC
circuit of the at least one LC circuit comprising an inductor and a
capacitor electrically in parallel, wherein the catheter is
configured such that, responsive to the force, either of the at
least one mass or each inductor of the at least one LC circuit is
displaceable within the catheter relative to the other of the at
least one mass or each inductor of the at least one LC circuit; and
control circuitry configured to: measure, for each of the at least
one LC circuit, a change in a resonance frequency of the LC circuit
based on a change in distance between the inductor and the at least
one mass, the change in distance responsive to the force; and
calculate at least one parameter of the force based on the change
in the resonance frequency.
2. The system of claim 1, wherein the at least one parameter
comprises a magnitude and a direction of the force.
3. The system of claim 2, further comprising a display, wherein the
control circuitry is configured to graphically indicate on the
display the magnitude and the direction of the force.
4. The system of claim 1, wherein the catheter further comprises a
spring element located between each inductor of the at least one LC
circuit and the at least one mass.
5. The system of claim 4, wherein the spring element is configured
to: permit the change in distance between each inductor of the at
least one LC circuit and the at least one mass; and resiliently
reverse the change in distance upon removal of the force from the
catheter.
6. The system of claim 4, wherein the control circuitry is
configured to calculate the parameter of the force by using a
function which relates the change in resonance frequency to the
change in distance.
7. The system of claim 4, wherein the control circuitry is
configured to calculate the parameter of the force by using a
constant which relates the change in the change in distance to a
value of the parameter of the force.
8. The system of claim 1, wherein the at least one LC circuit
comprises three LC circuits, the three LC circuits
circumferentially arrayed within the catheter.
9. The system of claim 1, wherein the high magnetic permeability
material has a relative permeability greater than 1500.
10. The system of claim 1, wherein the at least one mass of high
magnetic permeability material is passive and is not configured to
be electrically energized in connection with measuring the
force.
11. The system of claim 1, further comprising an additional mass of
high magnetic permeability material, wherein the at least one mass
is positioned either of proximal or distal with respect to the at
least one LC circuit and the additional mass is positioned the
other of proximal or distal with respect to the at least one LC
circuit, and wherein the catheter is configured such that the
additional mass is not displaceable within the catheter relative to
each inductor of the at least one LC circuit.
12. The system of claim 1, wherein for each of the at least one LC
circuit, the control circuitry is configured to deliver a
continuous waveform, wherein the continuous waveform causes the LC
circuit to oscillate; and the control circuitry is configured to
measure the change in the resonance frequency by analyzing the
oscillation in the LC circuit and determining whether the
oscillation changes in frequency between pulses of the plurality of
pulses.
13. The system of claim 1, further comprising a printed circuit
board, wherein each of the at least one LC circuit is mounted on
the printed circuit board.
14. The system of claim 13, wherein each inductor of the at least
one LC circuit comprises a conductor formed into a flat radial
spiral.
15. The system of claim 1, wherein, for each of the at least one LC
circuit, the control circuitry is configured to deliver a plurality
of pulses, wherein each pulse causes the LC circuit to oscillate,
and the control circuitry is configured to measure the change in
the resonance frequency by analyzing the oscillation in the LC
circuit and determining whether the oscillation changes in
frequency between pulses of the plurality of pulses.
16. The system of claim 1, wherein, for each LC circuit of the
plurality of LC circuits, the inductance of the LC circuit changes
based on the proximity of the at least one mass to the inductor of
the circuit.
17. A system for measuring a force within a body, the system
comprising: a catheter comprising at least one sensor, at least one
mass of high magnetic permeability material, and at least one
spring element configured to permit movement within the catheter
between the at least one sensor and the at least one mass
responsive to the force; and control circuitry configured to:
measure, for each sensor, a change in a resonance frequency of the
sensor based on a change in distance between the sensor and the at
least one mass, the change in distance responsive to the force; and
calculate at least one parameter of the force based on the change
in the resonance frequency.
18. The system of claim 17, further comprising a display, wherein
the at least one parameter comprises a magnitude and a direction of
the force and the control circuitry is configured to graphically
indicate on the display the magnitude and the direction of the
force.
19. The system of claim 17, wherein the control circuitry is
configured to calculate the at least one parameter of the force
based at least in part on a spring constant for the spring
element.
20. A system for measuring a force within a body, the system
comprising: a catheter comprising at least one sensor and an
element located within the catheter, the element displaceable
within the catheter relative to the at least one sensor; and
control circuitry configured to: measure, for each of the at least
one sensor, a change in a resonance frequency of the sensor based
on a change in distance between the sensor and the element, the
change in distance responsive to the force; calculate at least one
parameter of the force based on the change in the resonance
frequency; and output an indication of the at least one parameter
of the force.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to Provisional Application
No. 62/202,324, filed Aug. 7, 2015, which is herein incorporated by
reference in its entirety.
TECHNICAL FIELD
[0002] The present disclosure relates generally to various force
sensing catheter features.
BACKGROUND
[0003] In ablation therapy, it may be useful to assess the contact
between the ablation element and the tissue targeted for ablation.
In interventional cardiac electrophysiology (EP) procedures, for
example, the contact can be used to assess the effectiveness of the
ablation therapy being delivered. Other catheter-based therapies
and diagnostics can be aided by knowing whether a part of the
catheter contacts targeted tissue, and to what degree the part of
the catheter presses on the targeted tissue. The tissue exerts a
force back on the catheter, which can be measured to assess the
contact and the degree to which the catheter presses on the
targeted tissue.
[0004] The present disclosure concerns, among other things, systems
for measuring a force with a catheter.
SUMMARY
[0005] The present disclosure relates to devices, systems, and
methods for measuring a force experienced by a catheter.
[0006] Example 1 is a system for measuring a force within a body,
the system including a catheter and control circuitry. The catheter
includes at least one sensor and at least one mass of high magnetic
permeability material. The catheter is configured such that,
responsive to the force, the at least one mass is displaceable
within the catheter relative to the at least one sensor. The
control circuitry is configured to measure, for each sensor, a
change in a resonance frequency of the sensor based on a change in
distance between the sensor and the at least one mass, the change
in distance responsive to the force; and to calculate at least one
parameter of the force based on the change in the resonance
frequency.
[0007] In Example 2, the system of Example 1, further comprising a
display, wherein the at least one parameter comprises a magnitude
and a direction of the force and the control circuitry is
configured to graphically indicate on the display the magnitude and
the direction of the force.
[0008] In Example 3, the system of either of Examples 1 or 2,
wherein the high magnetic permeability material has a relative
permeability greater than 1500.
[0009] In Example 4, the system of any of Examples 1-3, wherein the
at least one mass of high magnetic permeability material is passive
and is not configured to be electrically energized in connection
with measuring the force.
[0010] In Example 5, the system of any of Examples 1-4, wherein
each of the at least one sensor includes an LC circuit, each at
least one LC circuit comprising an inductor and a capacitor which
are electrically in parallel, wherein the catheter is configured
such that, responsive to the force, either of the at least one mass
or each inductor of the at least one LC circuit is displaceable
within the catheter relative to the other of the at least one mass
or each inductor of the at least one LC circuit.
[0011] In Example 6, the system Example 5, wherein the control
circuitry is configured to measure, for each of the at least one
sensor, the change in the resonance frequency of the sensor based
on a change in distance between the inductor of the at least one LC
circuit and the at least one mass, the change in distance
responsive to the force.
[0012] In Example 7, the system of either of the Examples 5 or 6,
wherein the catheter further comprises a spring element located
between each inductor of the at least one LC circuit and the at
least one mass.
[0013] In Example 8, the system of Example 7, wherein the spring
element is configured to permit the change in distance between each
inductor of the at least one LC circuit and the at least one mass,
and resiliently reverse the change in distance upon removal of the
force from the catheter.
[0014] In Example 9, the system of any of Examples 5-8, wherein the
at least one LC circuit comprises three LC circuits, the three LC
circuits circumferentially arrayed within the catheter.
[0015] In Example 10, the system of any of Examples 5-9, further
comprising an additional mass of high magnetic permeability
material, wherein the at least one mass is positioned either of
proximal or distal with respect to the at least one LC circuit and
the additional mass is positioned the other of proximal or distal
with respect to the at least one LC circuit, and wherein the
catheter is configured such that the additional mass is not
displaceable within the catheter relative to each inductor of the
at least one LC circuit.
[0016] In Example 11, the system of any of Examples 5-10, further
comprising a printed circuit board, where each of the at least one
LC circuit is mounted on the printed circuit board.
[0017] In Example 12, the system of Example 11, wherein each
inductor of the at least one LC circuit comprises a conductor
formed into a flat radial spiral.
[0018] In Example 13, the system of any of Examples 5-12, wherein,
for each of the at least one LC circuit, the control circuitry is
configured to deliver a plurality of pulses, wherein each pulse
causes the LC circuit to oscillate, and the control circuitry is
configured to measure the change in the resonance frequency by
analyzing the oscillation in the LC circuit and determining whether
the oscillation changes in frequency between pulses of the
plurality of pulses.
[0019] In Example 14, the system of any of Examples 5-12, wherein
for each of the at least one LC circuit, the control circuitry is
configured to deliver a continuous waveform, wherein the continuous
waveform causes the LC circuit to oscillate; and the control
circuitry is configured to measure the change in the resonance
frequency by analyzing the oscillation in the LC circuit and
determining whether the oscillation changes in frequency between
pulses of the plurality of pulses.
[0020] In Example 15, the system of any of Examples 5-14, wherein,
for each LC circuit of the plurality of LC circuits, the inductance
of the LC circuit changes based on the proximity of the at least
one mass to the inductor of the LC circuit.
[0021] Example 16 is a system for measuring a force within a body,
the system including a catheter and control circuitry. The catheter
includes at least one LC circuit and at least one mass of high
magnetic permeability material. Each LC circuit of the at least one
LC circuit includes an inductor and a capacitor electrically in
parallel, wherein the catheter is configured such that, responsive
to the force, either of the at least one mass or each inductor of
the at least one LC circuit is displaceable within the catheter
relative to the other of the at least one mass or each inductor of
the at least one LC circuit. The control circuitry is configured to
measure, for each of the at least one LC circuit, a change in a
resonance frequency of the LC circuit based on a change in distance
between the inductor and the at least one mass, the change in
distance responsive to the force; and to calculate at least one
parameter of the force based on the change in the resonance
frequency.
[0022] In Example 17, the system of Example 16, wherein the at
least one parameter comprises a magnitude and a direction of the
force.
[0023] In Example 18, the system of Example 17, further comprising
a display, wherein the control circuitry is configured to
graphically indicate on the display the magnitude and the direction
of the force.
[0024] In Example 19, the system of any of Examples 16-18, wherein
the catheter further comprises a spring element located between
each inductor of the at least one LC circuit and the at least one
mass.
[0025] In Example 20, the system of Example 19, wherein the spring
element is configured to permit the change in distance between each
inductor of the at least one LC circuit and the at least one mass,
and to resiliently reverse the change in distance upon removal of
the force from the catheter.
[0026] In Example 21, the system of either of Examples 19 or 20,
wherein the control circuitry is configured to calculate the
parameter of the force by using a function which relates the change
in resonance frequency to the change in distance.
[0027] In Example 22, the system of any of Examples 19-21, wherein
the control circuitry is configured to calculate the parameter of
the force by using a constant which relates the change in the
change in distance to a value of the parameter of the force.
[0028] In Example 23, the system of any of Examples 16-22, wherein
the at least one LC circuit comprises three LC circuits, the three
LC circuits circumferentially arrayed within the catheter.
[0029] In Example 24, the system of any of Examples 16-23, wherein
the high magnetic permeability material has a relative permeability
greater than 1500.
[0030] In Example 25, the system of any of Examples 16-24, wherein
the at least one mass of high magnetic permeability material is
passive and is not configured to be electrically energized in
connection with measuring the force.
[0031] In Example 26, the system of any of Examples 16-25, further
comprising an additional mass of high magnetic permeability
material, wherein the at least one mass is positioned either of
proximal or distal with respect to the at least one LC circuit and
the additional mass is positioned the other of proximal or distal
with respect to the at least one LC circuit, and wherein the
catheter is configured such that the additional mass is not
displaceable within the catheter relative to each inductor of the
at least one LC circuit.
[0032] In Example 27, the system of any of Examples 16-25, wherein
for each of the at least one LC circuit, the control circuitry is
configured to deliver a continuous waveform, wherein the continuous
waveform causes the LC circuit to oscillate; and the control
circuitry is configured to measure the change in the resonance
frequency by analyzing the oscillation in the LC circuit and
determining whether the oscillation changes in frequency between
pulses of the plurality of pulses.
[0033] In Example 28, the system of any of Examples 16-27, further
comprising a printed circuit board, where each of the at least one
LC circuit is mounted on the printed circuit board.
[0034] In Example 29, the system of Example 28, wherein each
inductor of the at least one LC circuit comprises a conductor
formed into a flat radial spiral.
[0035] In Example 30, the system of any of Examples 16-29, wherein,
for each of the at least one LC circuit, the control circuitry is
configured to deliver a plurality of pulses, wherein each pulse
causes the LC circuit to oscillate, and the control circuitry is
configured to measure the change in the resonance frequency by
analyzing the oscillation in the LC circuit and determining whether
the oscillation changes in frequency between pulses of the
plurality of pulses.
[0036] In Example 31, the system of any of Examples 16-30, wherein,
for each LC circuit of the plurality of LC circuits, the inductance
of the LC circuit changes based on the proximity of the at least
one mass to the inductor of the circuit.
[0037] Example 32 is a system for measuring a force within a body,
the system including a catheter and control circuitry. The catheter
includes at least one sensor, at least one mass of high magnetic
permeability material, and at least one spring element. The spring
element is configured to permit movement within the catheter
between the at least one sensor and the at least one mass
responsive to the force. The control circuitry is configured to
measure, for each sensor, a change in a resonance frequency of the
sensor based on a change in distance between the sensor and the at
least one mass, the change in distance responsive to the force; and
to calculate at least one parameter of the force based on the
change in the resonance frequency.
[0038] In Example 33, the system of Example 31, wherein the at
least one parameter comprises a magnitude and a direction of the
force and the control circuitry is configured to graphically
indicate on the display the magnitude and the direction of the
force.
[0039] In Example 34, the system of either Examples 32 or 33,
wherein the control circuitry is configured to calculate the at
least one parameter of the force based at least in part on a spring
constant for the spring element.
[0040] Example 35 is a system for measuring a force within a body,
the system including a catheter and control circuitry. The catheter
includes at least one sensor and an element located within the
catheter. The element is displaceable within the catheter relative
to the at least one sensor. The control circuitry is configured to
measure, for each of the at least one sensor, a change in a
resonance frequency of the sensor based on a change in distance
between the sensor and the element, the change in distance
responsive to the force; calculate at least one parameter of the
force based on the change in the resonance frequency; and output an
indication of the at least one parameter of the force
[0041] While multiple embodiments are disclosed, still other
embodiments of the present invention will become apparent to those
skilled in the art from the following detailed description, which
shows and describes various illustrative embodiments of the present
disclosure. Accordingly, the drawings and detailed description are
to be regarded as illustrative in nature and not restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] FIGS. 1A-C show a system for measuring a force with a
catheter in accordance with various embodiments of this
disclosure.
[0043] FIG. 2 shows a block diagram of circuitry for controlling
various functions described herein.
[0044] FIG. 3 shows a detailed perspective view of a distal end of
a catheter in accordance with various embodiments of this
disclosure.
[0045] FIG. 4 shows a perspective view of the inside of a catheter
in accordance with various embodiments of this disclosure.
[0046] FIG. 5 shows a perspective view of a force measurement
assembly that can be housed within a catheter in accordance with
various embodiments of this disclosure.
[0047] FIG. 6 shows a perspective view of a sensor support in
accordance with various embodiments of this disclosure.
[0048] FIGS. 7A-7C show alternative embodiments of spring element
in accordance with various embodiments of this disclosure.
[0049] FIG. 8 shows a perspective view of a portion of a force
measurement assembly in accordance with various embodiments of this
disclosure.
[0050] FIG. 9 shows a printed circuit board containing three LC
circuits which operate as components of force sensors in accordance
with various embodiments of this disclosure.
[0051] FIG. 10 is a schematic illustration showing operational
aspects of a force measurement assembly in accordance with various
embodiments of this disclosure.
[0052] FIG. 11 is a schematic circuit diagram for supporting force
sensing functionality in accordance with various embodiments of
this disclosure.
[0053] FIG. 12 is another schematic circuit diagram for supporting
force sensing functionality in accordance with various embodiments
of this disclosure.
[0054] While the scope of the present disclosure is amenable to
various modifications and alternative forms, specific embodiments
have been shown by way of example in the drawings and are described
in detail below. The intention, however, is not to limit the scope
of the invention to particular embodiments described and/or shown.
On the contrary, the invention is intended to cover all
modifications, equivalents, and alternatives falling within the
scope of the appended claims.
DETAILED DESCRIPTION
[0055] Various cardiac abnormalities can be attributed to improper
electrical activity of cardiac tissue. Such improper electrical
activity can include, but is not limited to, generation of
electrical signals, conduction of electrical signals, and/or
mechanical contraction of the tissue in a manner that does not
support efficient and/or effective cardiac function. For example,
an area of cardiac tissue may become electrically active
prematurely or otherwise out of synchrony during the cardiac cycle,
thereby causing the cardiac cells of the area and/or adjacent areas
to contract out of rhythm. The result is an abnormal cardiac
contraction that is not timed for optimal cardiac output. In some
cases, an area of cardiac tissue may provide a faulty electrical
pathway (e.g., a short circuit) that causes an arrhythmia, such as
atrial fibrillation or supraventricular tachycardia. In some cases,
inactivated tissue (e.g., scar tissue) may be preferable to
malfunctioning cardiac tissue.
[0056] Cardiac ablation is a procedure by which cardiac tissue is
treated to inactivate the tissue. The tissue targeted for ablation
may be associated with improper electrical activity, as described
above. Cardiac ablation can lesion the tissue and prevent the
tissue from improperly generating or conducting electrical signals.
For example, a line, a circle, or other formation of lesioned
cardiac tissue can block the propagation of errant electrical
signals. In some cases, cardiac ablation is intended to cause the
death of cardiac tissue and to have scar tissue reform over the
lesion, where the scar tissue is not associated with the improper
electrical activity. Lesioning therapies include electrical
ablation, radio frequency ablation, cyroablation, microwave
ablation, laser ablation, and surgical ablation, among others.
While cardiac ablation therapy is referenced herein as an exemplar,
various embodiments of the present disclosure can be directed to
ablation of other types of tissue and/or to non-ablation diagnostic
and/or catheters that deliver other therapies.
[0057] Ideally, an ablation therapy can be delivered in a minimally
invasive manner, such as with a catheter introduced to the heart
through a vessel, rather than surgically opening the heart for
direct access (e.g., as in a maze surgical procedure). For example,
a single catheter can be used to perform an electrophysiology study
of the inner surfaces of a heart to identify electrical activation
patterns. From these patterns, a clinician can identify areas of
inappropriate electrical activity and ablate cardiac tissue in a
manner to kill or isolate the tissue associated with the
inappropriate electrical activation. However, the lack of direct
access in a catheter-based procedure may require that the clinician
only interact with the cardiac tissue through a single catheter and
keep track of all of the information that the catheter collects or
is otherwise associated with the procedure. In particular, it can
be challenging to determine the location of the therapy element
(e.g., the proximity to tissue), the quality of a lesion, and
whether the tissue is fully lesioned, under-lesioned (e.g., still
capable of generating and/or conducting unwanted electrical
signals), or over-lesioned (e.g., burning through or otherwise
weakening the cardiac wall). The quality of the lesion can depend
on the degree of contact between the ablation element and the
targeted tissue. For example, an ablation element that is barely
contacting tissue may not be adequately positioned to deliver
effective ablation therapy. Conversely, an ablation element that is
pressed too hard into tissue may deliver too much ablation energy
or cause a perforation of the cardiac wall.
[0058] The present disclosure concerns, among other things,
methods, devices, and systems for assessing a degree of contact
between a part of a catheter (e.g., an ablation element) and
tissue. Knowing the degree of contact, such as the magnitude and
the direction of a force generated by contact between the catheter
and the tissue, can be useful in determining the degree of
lesioning of the targeted tissue. Information regarding the degree
of lesioning of cardiac tissue can be used to determine whether the
tissue should be further lesioned or whether the tissue was
successfully ablated, among other things. Additionally or
alternatively, an indicator of contact can be useful when
navigating the catheter because a user may not feel a force being
exerted on the catheter from tissue as the catheter is advanced
within a patient, thereby causing vascular or cardiac tissue damage
or perforation.
[0059] FIGS. 1A-C is an illustrative embodiment of a system 100 for
sensing data from inside the body and/or delivering therapy. For
example, the system 100 can be configured to map cardiac tissue
and/or ablate the cardiac tissue, among other options. The system
100 includes a catheter 110 connected to a control unit 120 via
handle 114. The catheter 110 can comprise an elongated tubular
member having a proximal end 115 connected with the handle 114 and
a distal end 116 configured to be introduced within a heart 101 or
other area of the body. As shown in FIG. 1A, the distal end 116 of
the catheter 110 is within the left atrium.
[0060] As shown in the window 118 of FIG. 1B, the distal end 116 of
the catheter 110 includes a proximal segment 111, a spring segment
112, and a distal segment 113. The distal segment 113, or any other
segment, can be in the form of an electrode configured for sensing
electrical activity, such as electrical cardiac signals. Such an
electrode (or other electrode on the catheter 110) can additionally
or alternatively be used to deliver ablative energy to tissue.
[0061] The proximal segment 111, the spring segment 112, and the
distal segment 113 can be coaxially aligned with each other in a
base orientation as shown in FIG. 1B. Specifically, each of the
proximal segment 111, the spring segment 112, and the distal
segment 113 are coaxially aligned with a common longitudinal axis
109. The longitudinal axis 109 can extend through the radial center
of each of the proximal segment 111, the spring segment 112, and
the distal segment 113, and can extend through the radial center of
the distal end 116 as a whole. In some embodiments, the coaxial
alignment of the proximal segment 111 with the distal segment 113
can correspond to the base orientation. As shown, the distal end
116, at least along the proximal segment 111, the spring segment
112, and the distal segment 113, extends straight. In some
embodiments, this straight arrangement of the proximal segment 111,
the spring segment 112, and the distal segment 113 can correspond
to the base orientation. The proximal segment 111, the spring
segment 112, and the distal segment 113 can be mechanically biased
to assume the base orientation.
[0062] A force measurement assembly 108 can reside within the
distal end 116 of the catheter 110. The force measurement assembly
108 can extend from the proximal segment 111, through the spring
segment 112, to the distal segment 113. While a single force
measurement assembly 108 is shown in FIGS. 1B-C, a plurality of
force measurement assemblies can be provided and each can be
configured in any manner as the force measurement assembly 108 as
described herein. The force measurement assembly 108 can
mechanically support the distal segment 113 relative to the
proximal segment 111. For example, the force measurement assembly
108 can provide most or all of the mechanical support that holds
the distal segment 113 in the base orientation with respect to the
proximal segment 111. In some embodiments, it is the force
measurement assembly 108 which can provide the resilient spring
properties of the spring segment 112. A proximal end of the force
measurement assembly 108 can be anchored in the proximal segment
111 while a distal end of the force measurement assembly 108 can be
anchored within the distal segment 113. For example, the proximal
end of the force measurement assembly 108 can be rigidly attached
to material within the proximal segment 111 while the distal end of
the force measurement assembly 108 can be rigidly attached to
material within the distal segment 113. The force measurement
assembly 108 can be generally elongated from the proximal segment
111 to the distal segment 113.
[0063] The catheter 110 includes force sensing capabilities. For
example, the catheter 110 is configured to sense a force due to
engagement with tissue 117. The distal segment 113 can be
relatively rigid while segments proximal of the distal segment 113
can be relatively flexible. In particular, the spring segment 112
may be more flexible than the distal segment 113 and the proximal
segment 111 such that when the distal end 116 of the catheter 110
engages tissue 117, the spring segment 112, as shown in FIG. 1C,
bends. For example, the distal end 116 of the catheter 110 can be
generally straight as shown in FIG. 1B. When the distal segment 113
engages tissue 117, the distal end 116 of the catheter 110 can bend
at the spring segment 112 such that the distal segment 113 moves
relative to the proximal segment 111. As shown in FIGS. 1B and 1C,
the normal force from the tissue moves the distal segment 113 out
of coaxial alignment (e.g., with respect to the longitudinal axis
109) with the proximal segment 111 while the spring segment 112
bends. As such, proximal segment 111 and the distal segment 113 may
be stiff to not bend due to the force while the spring segment 112
may be less stiff and bend to accommodate the force exerted on the
distal end 116 of the catheter 110.
[0064] The force measurement assembly 108, which extends through or
around the spring segment 112, can be used to determine the
magnitude and the direction of the force due to engagement with the
tissue 117. As shown in FIG. 1C, the distal segment 113 has moved
relative to the proximal segment 111, thereby straining the force
measurement assembly 108. Specifically, the force measurement
assembly 108 is shown to be bending relative to the base
orientation of the force measurement assembly 108 shown in FIG. 1B.
The force measurement assembly 108 can be configured to sense such
bending. The bending can change one or more electrical properties
of the force measurement assembly 108. As further discussed herein,
the force measurement assembly 108 can include an LC circuit that
changes in resonance frequency in proportion to the bending, the
bending being proportional to the force per Hooke's law. As such,
by measuring a change in resonance frequency of one sensor, a
parameter of the force, such as a magnitude of the force, can be
determined for one axis. Three LC circuit-based sensors can be
provided within the force measurement assembly 108 to characterize
the bending, and therefore the force, in three axes (X, Y, and Z)
to determine parameters of the force, such as the magnitude and
direction of the force in three-dimensional space. These and other
aspects are further discussed herein.
[0065] The control unit 120 of the system 100 includes a display
121 (e.g., LCD) for displaying information. The control unit 120
further includes a user input 122 which can comprise one or more
buttons, toggles, a track ball, a mouse, touchpad, or the like for
receiving user input. The user input 122 can additionally or
alternatively be located on the handle 114. The control unit 120
can contain control circuitry for performing the functions
referenced herein. Some or all of the control circuitry can
alternatively be located within the handle 114.
[0066] FIG. 2 illustrates a block diagram showing an example of
control circuitry which can perform functions referenced herein.
This or other control circuitry can be housed within control unit
120, which can comprise a single housing or multiple housings among
which components are distributed. Control circuitry can
additionally or alternatively be housed within the handle 114. The
components of the control unit 120 can be powered by a power supply
(not shown, but known in the art), which can supply electrical
power to any of the components of the control unit 120 and the
system 100. The power supply can plug into an electrical outlet
and/or provide power from a battery, among other options.
[0067] The control unit 120 can include a catheter interface 123.
The catheter interface 123 can include a plug which receives an
electrical cable from the handle 114. The catheter 110 can include
multiple conductors (not shown, but known in the art) to convey
electrical signals between the distal end 116 and the proximal end
115 and further through handle 14 to the catheter interface 123. It
is through the catheter interface 123 that the control unit 120
(and/or the handle 114, if control circuitry is included in the
handle 114) can send electrical signals to any element within the
catheter 110 and/or receive an electrical signal from any element
within the catheter 110. The catheter interface 123 can conduct
signals to or from any of the components of the control unit
120.
[0068] The control unit 120 can include an ultrasound subsystem 124
which includes components for operating the ultrasound functions of
the system 100. While the illustrated example of control circuitry
shown in FIG. 2 includes the ultrasound subsystem 124, it will be
understood that not all embodiments may include ultrasound
subsystem 124 or any circuitry for imaging tissue. The ultrasound
subsystem 124 can include a signal generator configured to generate
a signal for ultrasound transmission and signal processing
components (e.g., a high pass filter) configured to filter and
process reflected ultrasound signals as received by an ultrasound
transducer in a sense mode and conducted to the ultrasound
subsystem 124 through a conductor in the catheter 110. The
ultrasound subsystem 124 can send signals to elements within the
catheter 110 via the catheter interface 123 and/or receive signals
from elements within the catheter 110 via the catheter interface
123.
[0069] The control unit 120 can include an ablation subsystem 125.
The ablation subsystem 125 can include components for operating the
ablation functions of the system 100. While the illustrated example
of control circuitry shown in FIG. 2 includes the ablation
subsystem 125, it will be understood that not all embodiments may
include ablation subsystem 125 or any circuitry for generating an
ablation therapy. The ablation subsystem 125 can include an
ablation generator to provide different therapeutic outputs
depending on the particular configuration (e.g., a high frequency
alternating current signal in the case of radio frequency ablation
to be output through one or more electrodes). Providing ablation
energy to target sites is further described, for example, in U.S.
Pat. No. 5,383,874 and U.S. Pat. No. 7,720,420, each of which is
expressly incorporated herein by reference in its entirety for all
purposes. The ablation subsystem 125 may support any other type of
ablation therapy, such as microwave ablation. The ablation
subsystem 125 can deliver signals or other type of ablation energy
through the catheter interface 123 to the catheter 110.
[0070] The control unit 120 can include a force sensing subsystem
126. The force sensing subsystem 126 can include components for
measuring a force experienced by the catheter 110 via the force
measurement assembly 108. The force sensing subsystem 126 can
include some of the components shown in FIGS. 11 and 12. Such
components can include signal processors, analog-to-digital
converters, operational amplifiers, transistors, comparators,
and/or any other circuitry for conditioning and measuring one or
more signals. The force sensing subsystem 126 can send signals to
elements within the catheter 110 via the catheter interface 123
and/or receive signals from elements within the catheter 110 via
the catheter interface 123.
[0071] Each of the ultrasound subsystem 124, the ablation subsystem
125, and the force sensing subsystem 126 can send signals to, and
receive signals from, the processor 127. The processor 127 can be
any type of processor for executing computer functions. For
example, the processor 127 can execute program instructions stored
within the memory 128 to carry out any function referenced herein,
such as determine the magnitude and direction of a force
experienced by the catheter 110.
[0072] The control unit 120 further includes an input/output
subsystem 129 which can support user input and output
functionality. For example, the input/output subsystem 129 may
support the display 121 to display any information referenced
herein, such as a graphic representation of tissue, the catheter
110, and a magnitude and direction of the force experienced by the
catheter 110, among other options. Input/output subsystem 129 can
log key and/or other input entries via the user input 122 and route
the entries to other circuitry.
[0073] A single processor 127, or multiple processors, can perform
the functions of one or more subsystems, and, as such, the
subsystems may share control circuitry. Although different
subsystems are presented herein, circuitry may be divided between a
greater or lesser number of subsystems, which may be housed
separately or together. In various embodiments, circuitry is not
distributed between subsystems, but rather is provided as a unified
computing system. Whether distributed or unified, the components
can be electrically connected to coordinate and share resources to
carry out functions.
[0074] FIG. 3 illustrates a detailed view of a distal end 116 of a
catheter 110. FIG. 3 shows a catheter shaft 180. The catheter shaft
180 can extend from the distal segment 113 to the handle 114, and
thus can define an exterior surface of the catheter 110 along the
spring segment 112, the proximal segment 111, and further
proximally to the proximal end 115. The catheter shaft 180 can be a
polymeric tube formed from various polymers, such as polyurethane,
polyamide, polyether block amide, silicone, and/or other materials.
In some embodiments, the catheter shaft 180 may be relatively
flexible, and at least along the spring segment 112 may not provide
any material mechanical support to the distal segment 113 (e.g.,
facilitated by thinning of the wall of the catheter shaft 180 along
the spring segment 112). Alternatively, the catheter shaft 180 may
provide structural mechanical support to the distal segment 113
relative to the spring segment 112 and the proximal segment
111.
[0075] As shown, the proximal segment 111 can be proximal and
adjacent to the spring segment 112. The length of the proximal
segment 111 can vary between different embodiments, and can be five
millimeters to five centimeters, although different lengths are
also possible. The length of the spring segment 112 can also vary
between different embodiments, and can be dependent on the length
of the force measurement assembly 108 as a whole or specifically on
a spring element within the force measurement assembly 108. The
spring segment 112 is adjacent to the distal segment 113. As shown
in FIG. 3, the distal segment 113 can be defined by an electrode
181. The electrode 181 can be an ablation electrode. In some other
embodiments, the distal segment 113 may not be an electrode. The
electrode 181 can be in a shell form which can contain other
components. The electrode 181 can include a plurality of ports 182.
One or more ultrasonic transducers, housed within the electrode
181, can transmit and receive signals through the ports 182 or
through additional dedicated ports in the tip shell. Additionally,
or in place of the transducers, one or more miniature electrodes
(not shown) may be incorporated into the tip shell assembly.
[0076] FIG. 4 shows the catheter 110 after the removal of the
catheter shaft 180 to expose various components that underlie the
catheter shaft 180. The removal of the catheter shaft 180 exposes
structural and force sensing components. The components can include
a proximal hub 184, a distal hub 185, and a force measurement
assembly 108 that bridges between the proximal hub 184 and the
distal hub 185. The proximal hub 184 and the distal hub 185 can be
respective rings to which the force measurement assembly 108 is
attached proximally and distally, respectively. One or both of the
proximal hub 184 and the distal hub 185 can be formed from
electrically insulative material, such as polymer (e.g.,
polyethylene or polyether ether ketone); an electrically conductive
material, such as a metal (e.g., stainless steel, titanium, or
aluminum); and/or a composite or ceramic material.
[0077] The proximal hub 184 and the distal hub 185 can be coaxially
aligned with respect to the longitudinal axis 109. For example, the
longitudinal axis 109 can extend through the respective radial
centers of each of the proximal hub 184 and the distal hub 185. One
or more inner tubes 186 (one shown) can extend through the catheter
110 (e.g., to the handle 114), through the proximal hub 184 and the
distal hub 185. The inner tube 186 can include one or more lumens
within which one or more conductors can extend from the proximal
end 115 to the distal segment 113, such as for connecting with one
or more electrical elements (e.g., ultrasound transducer,
electrode, the force measurement assembly 108, or other component).
Coolant fluid can additionally or alternatively be routed through
the inner tube 186, or through an additional inner tube 186. In
various embodiments, the catheter 110 is open irrigated (e.g.,
through the plurality of ports 182) to allow the coolant fluid to
flow out of the distal segment 113. Various other embodiments
concern a non-irrigated catheter 110.
[0078] A tether 183 can attach to a proximal end of the proximal
hub 184. The tether 183 can attach to a deflection mechanism within
a handle to cause deflection of the distal end 116. A knob, slider,
or plunger on a handle may be used to create tension or slack in
the tether 183.
[0079] As shown in FIG. 4, the spring segment 112 can extend from a
distal edge of the proximal hub 184 to a proximal edge of the
distal hub 185. As such, the proximal hub 184 can be part of, and
may even define the length of, the proximal segment 111. Likewise,
the distal hub 185 can be part of the distal segment 113. The
proximal hub 184 and the distal hub 185 can be stiffer than the
force measurement assembly 108 such that a force directed on the
distal segment 113 causes the distal end 116 to bend along the
force measurement assembly 108 (the spring segment 112
specifically) rather than along the distal segment 113 or the
proximal segment 111. Even within the force measurement assembly
108, the bending may be isolated to an expanse of a spring element
further discussed herein. The distal segment 113 may be
mechanically maintained in a base orientation with respect to the
longitudinal axis 109 mostly or entirely by the force measurement
assembly 108 (e.g., wherein all other components contribute
negligible or no mechanical support of the distal segment 113
relative the proximal segment 111). In some other embodiments,
other elements can provide mechanical support to the distal segment
113, such as the catheter shaft 180 and/or internal struts.
[0080] The proximal end of the force measurement assembly 108 can
be attached to the distal end of the proximal hub 184, such as by a
press fit feature, an adhesive (e.g., epoxy), welding, staking,
pinning, and/or riveting. The distal end of the force measurement
assembly 108 can be attached to the proximal end of the distal hub
185, such as by a press fit feature, an adhesive (e.g., epoxy),
welding, staking, pinning, and/or riveting. It is noted that each
of the proximal hub 184, the force measurement assembly 108, and
the distal hub 185 can include coaxial lumens that allow the inner
tube 186 or other element to extend within the lumens of the
proximal hub 184, the force measurement assembly 108, and the
distal hub 185 to the distal segment 113 and the electrode 181. The
conductors (not illustrated) can be routed through the inner tube
186 from one or more elements along the distal segment 113 to a
proximal end of the catheter 110 for delivering signals to and/or
from control circuitry. The conductors can be copper wires
insulated by a polymer coating, or can be similar conductive
elements.
[0081] A tail 136 extends from the force measurement assembly 108
in a proximal direction. The tail 136 can be a plurality of
individual insulated conductors, or part of a printed circuit board
that includes a plurality of conductors. The tail 136 can extend
further proximally to the proximal end 115 of the catheter 110 to
electrically connect with the control circuitry. The tail 136 can
alternatively be routed within the lumens within the force
measurement assembly 108, the proximal hub 184, and/or the inner
tube 186. However, as shown, the tail 136 extends within the
catheter shaft 180 but outside of the force measurement assembly
108, the proximal hub 184, and the catheter shaft 180.
[0082] FIG. 5 shows a perspective view of the force measurement
assembly 108 isolated from the other components of the catheter
110. The force measurement assembly 108 is in a generally tubular
shape and includes a lumen 137 that extends the full-length of the
force measurement assembly 108. As such, in some embodiments, all
sensory components of the force measurement assembly 108 can be
contained in a tubular wall of the force measurement assembly
108.
[0083] The force measurement assembly 108 is shown to include a
proximal support 130. A proximal end of the proximal support 130
can attach to a distal end of the proximal hub 184. In some
embodiments, the proximal hub 184 and the proximal support 130 are
unified into a single element, but in the present example are shown
as separate elements. The force measurement assembly 108 is shown
to include a distal support 131. A distal end of the distal support
131 can attach to a proximal end of the distal hub 185. In some
embodiments, the distal hub 185 and the distal support 131 are
unified into a single element, but in the present example are shown
as separate elements. The proximal support 130 and the distal
support 131 can each be formed from polymer (e.g., polyethylene,
polyether ether ketone, or polyoxymethylene), a metal (e.g.,
stainless steel, aluminum, or nitinol), or a ceramic. In some
embodiments, the proximal support 130 and the distal support 131
are each configured to not compress when the force is applied to
the catheter 110. In other words, the proximal support 130 and the
distal support 131 (as well as the proximal hub 184 and the distal
hub 185) pass all forces through themselves and do not strain under
stress.
[0084] The force measurement assembly 108 is further shown to
include a proximal mass 132 and a distal mass 133. The proximal
mass 132 can be attached to a distal end of the proximal support
130. The distal mass 133 can be attached to a proximal end of the
distal support 131. Such attachments can be made with an adhesive
such as epoxy adhesive, or by welding, staking, pinning, or
riveting. Each of the masses 132, 133 can be in the shape of a ring
that is consistent with the tubular profile of the force
measurement assembly 108 (e.g., by having the same inner diameter
and outer diameter of the tubular structure of the force
measurement assembly 108). While each of the proximal mass 132 and
the distal mass 133 are shown as respective unitary elements (in
this case, rings), each mass could be comprised of the same type of
material but comprise several distinct masses supported in a ring
structure. For example, a plurality of masses can be embedded
within the distal end of the proximal support 130, the plurality of
masses arrayed circumferentially about the lumen 137. A plurality
masses can be embedded within the proximal end of the distal
support 131, the plurality masses arrayed circumferentially about
the lumen 137.
[0085] The proximal mass 132 and the distal mass 133 can be formed
from material having high magnetic permeability, such as ferrite.
In some embodiments, the high magnetic permeability material
forming proximal mass 132 and the distal mass 133 has a relative
permeability greater than 1500. The proximal mass 132 and the
distal mass 133 can be passive, such that each is not electrically
activated by current during any phase of force sensing. In some
cases, each of the proximal mass 132 and the distal mass 133 do not
emit an electromagnetic field. However, a mass material having a
high magnetic permeability can affect the emitted electromagnetic
field of other elements, as further shown herein.
[0086] The force measurement assembly 108 is further shown to
include a sensor support 134. The sensor support 134 can be a
printed circuit board. Such a printed circuit board can comprise a
flat, flexible sheet of a base polymer layer (e.g., polyimide), a
trace layer (e.g., a flat copper, gold, silver, or nickel
conductor), and a polymer cover coat (e.g., polyamide) over the
trace layer. In some embodiments, a greater number of layers can be
built from these components, such as overlapping but electrically
isolated trace layers.
[0087] FIG. 6 shows a perspective view of the sensor support 134.
The sensor support 134 includes a plurality of sensors 140. The
plurality of sensors 140 can be embedded within or mounted upon the
sensor support 134. Three sensors 140 are shown circumferentially
arrayed about the lumen 137. The use of three sensors 140 can be
advantageous for characterizing forces in three dimensions (e.g.,
along X, Y, and Z axes). It is noted that the plurality of sensors
140 are arrayed at 120.degree. about the circumference of the
sensor support 134. In other embodiments, more than three sensors
140 may employed, and the plurality of sensors 140 may be with
disposed in different uniform and non-uniform circumferential
arrangements. The sensor support 134 includes a tail 136 which can
be made from the same printed circuit board material as the rest of
the sensor support 134. The tail 136 can include a plurality of
conductors that electrically connect, respectively, with the
plurality of sensors and extend to a proximal end of the catheter
110 for connecting with different channels of control
circuitry.
[0088] As shown in FIG. 5, the force measurement assembly 108
further comprises a spring element 135. The spring element 135 is
positioned between the sensor support 134 and the distal mass 133.
The spring element 135 can be attached to any of the components of
the force measurement assembly 108, such as the proximal support
130, the distal support 131, the proximal mass 132, the distal mass
133, and/or the sensor support 134. In some embodiments, the spring
element 135 may connect the distal hub 185 to the proximal hub 184,
thereby controlling the relative displacement between the sensor
support 134 and the distal mass 133. In some embodiments, the force
measurement assembly 108 only bends along the spring element 135
such that the force measurement assembly 108 does not bend along
the proximal support 130, the distal support 131, the proximal mass
132, the distal mass 133, and the sensor support 134. The spring
element 135 can be configured to permit bending of the force
measurement assembly 108 (and the distal end 116 of the catheter
110 as shown in FIG. 1C) while resiliently returning the force
measurement assembly 108 (and the distal end 116 of the catheter
110) to the base orientation shown in FIG. 1B after removal of the
force. In some embodiments, the force measurement assembly 108 may
provide most or all of the mechanical support that holds the distal
segment 113 in the base orientation with respect to the proximal
segment 111 and resiliently returns the distal segment 113 to the
base orientation with respect to the proximal segment 111 after
removal of the force. In some of these embodiments, the spring
element 135 may provide most or all of the mechanical support that
holds the distal segment 113 in the base orientation with respect
to the proximal segment 111 and resiliently returns the distal
segment 113 to the base orientation with respect to the proximal
segment 111 after removal of the force. However, in some other
embodiments, the catheter shaft 180 may provide some or most of the
mechanical support for the distal segment 113 relative to the
proximal segment 111.
[0089] Each layer of the force measurement assembly 108 can be
attached to the adjacent layers of the force measurement assembly
108 by adhesive (e.g., epoxy) and/or a tube or layer of polymer
wrapped around the circumference of the force measurement assembly
108 to encase the force measurement assembly 108 and secure the
layers. In other embodiments, some or all of the layers may be
mechanically attached to one another by pinning or staking.
[0090] The spring element 135 can take different forms. FIG. 7A
shows a perspective view of one form. The spring element 135A of
FIG. 7A can be an elastomeric member. The elastomeric member can
have the same inner diameter and/or outer diameter as any other
components of the force measurement assembly 108. The spring
element 135A can be formed from rubber, silicone, or other
elastomeric polymer that can be compressed or stretched due to a
force and then can resiliently return to its original form after
removal of the force. FIG. 7B shows a spring element 135B as an
alternative design to that of FIG. 7A. Specifically, the spring
element 135B is a coiled metal spring, which can be formed from
stainless steel or nitinol, for example. The coiled metal spring
can have the same inner diameter and/or outer diameter as any other
components of the force measurement assembly 108. FIG. 7C shows a
spring element 135C as an alternative design to that of FIGS. 7A
and 7B. Specifically, the spring element 135C is a cut, etched, or
formed metallic tubular element, which can be made from, for
example, stainless steel or nitinol. The metallic tubular element
can have the same inner diameter and/or outer diameter as any other
components of the force measurement assembly 108.
[0091] FIG. 8 shows a perspective view of a portion of another
embodiment of the force measurement assembly 108. FIG. 8 shows a
portion of the force measurement assembly 108, including the
proximal mass 132, the distal mass 133, the sensor support 134, and
the spring element 135. The proximal mass 132, the distal mass 133,
and the spring element 135 are formed as a combined element 138.
The curved portion of the combined element 138 connecting the
proximal mass 132 to the distal mass 133 forms the spring element
135. Three of the combined elements 138 can be circumferentially
arrayed around the sensor support 134, with one at each of the
sensors 140. In this way, the combined element 138 may capture and
contain most of the induced magnetic flux at the sensor 140, while
also providing the resiliency needed to allow for a change in the
resonance frequency of the sensor 140.
[0092] FIG. 9 shows an overhead sectional view of the sensor
support 134. The view of FIG. 9 shows circuit components as
exposed, wherein the circuit components may otherwise be normally
covered by insulation. Each sensor 140 comprises an LC circuit
composed of an inductor 151 and a capacitor 152 connected
electrically in parallel to each other. Each sensor 140 further
includes a switch 153 which can change an electrical connection to
the LC circuit from an exciter channel to a measurement channel, as
further discussed herein. While the switches 153 are included on
the sensor support 134, in some other embodiments the switches 153
are located elsewhere within the catheter 110, handle 114, or
control unit 120. It is noted that switches 153 can be replaced
with transformers in various embodiments.
[0093] The inductors 151 can be flat conductor spirals disposed
within the printed circuit board of the sensor support 134. As
such, the inductors 151 do not comprise helical coil windings, and
are therefore more compact. The electromagnetic field generated by
each flat conductor spiral may be particularly small, but such a
small field may be advantageous because it is easier to fill this
small field with high magnetic permeability material (as further
discussed herein) and because the small field minimizes the
potential sources of noise which may otherwise influence the
field.
[0094] In some other embodiments, the inductors 151 can include
helical windings. While each sensor 140 is shown as including one
inductor 151, two (or more) identical inductors can be provided for
each sensor 140 with the multiple inductors 151 serially
electrically connected. When multiple flat conductor spirals are
used, the multiple flat conductor spirals can be stacked on top of
each other while still being within the printed circuit board of
the sensor support 134. When connected in series, the inductances
of the stacked flat conductor spirals are additive. Alternatively,
the multiple inductors can be placed side-by-side. In other
embodiments, the inductors 151 can include an externally wound
inductive coil component that is attached to the sensor support 134
and electrically connected by, for example, solder or conductive
epoxy.
[0095] The sensors 140 can operate by exciting each LC circuit with
a pulse of energy. For example the switch 153 can connect to a
conductor which can transport a pulse of electrical energy to the
LC circuit. Once energized from the pulse, the LC circuit will
oscillate for a brief period of time. In particular, the LC circuit
will oscillate at its resonance frequency. The resonance frequency
of the LC circuit is governed by the relationship shown in Equation
1:
f=1/[2.pi. (LC)] Equation 1:
[0096] In Equation 1, the resonance frequency (f) of oscillation is
a function of an inductance (L) and a capacitance (C). As will be
explained further herein, the inductance of the LC circuit may vary
based on the proximity of the distal mass 133 of high magnetic
permeability material to the inductor 151, wherein the proximity is
variable based on the force applied to the catheter 110.
[0097] FIG. 10 is a schematic view of a portion of the force
measurement assembly 108. As discussed previously, the sensor
support 134 can include sensors 140 which themselves include
inductors 151. During oscillation of the LC circuit following
excitation from a pulse, the inductors 151 temporarily create
magnetic fields 141. Within the envelopes of the magnetic fields
141 are the proximal mass 132 and the distal mass 133, each formed
of high magnetic permeability material. The presence of the high
magnetic permeability material within the magnetic fields 141
increases the strength of these fields relative to other materials
and/or air. As shown in FIG. 9, the distance from the sensor
support 134 (containing the inductors 151) and the distal mass 133
of high magnetic permeability material is variable. The distance
can be made shorter by the force placed on the distal segment 113
of the catheter 110 compressing the spring element 135. Some forces
may compress one portion of the spring element 135 and elongate
another portion of the spring element 135, thereby bringing the
distal mass 133 of high magnetic permeability material closer to
one or more of the sensors 140 but further away from one or more of
the other sensors 140. In some other cases, the force may compress
different circumferential sections of the spring element 135 to
different degrees, such that one or more sensors 140 is brought
closer to the distal mass 133 than other sensors 140. In any case,
increasing or decreasing the amount of the distal mass 133 of high
magnetic permeability material within the fields 141 changes the
inductance of the LC circuits, which according to Equation 1
changes the resonance frequency of the LC circuits. As such, the
change in resonance frequency is proportional to the displacement
of the distal mass 133 of high magnetic permeability material
relative to the sensor support 134. The spring element 135 provides
predictable resistance to movement of the distal mass 133 relative
to the sensor support 134, a relationship governed by Hooke's law
(force=-kx, wherein k is a spring constant and x is displacement).
Therefore, a known displacement can be correlated to a force value
by using a spring constant value for the spring element 135. The
spring constant can be determined experimentally for each unit as
part of a calibration step or can be predetermined for each type of
spring element 135 and stored in a memory, such as memory 128
described above in reference to FIG. 2. In summary, the
displacement of the distal mass 133 relative to the sensor 140 is
proportional to the force placed on catheter 110. The displacement
of the distal mass 133 further results in a change in the
inductance (L) of the associated inductor 151, which results in a
change in the resonance frequency of the sensor 140 per Equation 1.
Multiple resonance frequency changes of multiple spatially
distributed sensors 140 can indicate the magnitude and direction of
the force in three dimensions. Such a force-frequency relationship
is represented by Equation 2:
F=-k(1[(2.pi.f).sup.2C]), Equation 2:
wherein is the function relating resonance frequency (f) to the
displacement (x) of the distal mass 133.
[0098] It is noted that operation of the sensors 140 do not involve
any of the sensors sensing a magnetic field broadcast from a remote
element within the catheter 110. Rather, each sensor 140 generates
its own magnetic field and changes in the magnetic field, due to
increasing or decreasing amounts of passive high magnetic
permeability material within the magnetic field, are sensed. This
minimizes the influence of noise on the sensor 140. Moreover, each
of the proximal mass 132 and the distal mass 133 of high magnetic
permeability material help to shield the sensors 140 from
electromagnetic noise.
[0099] In some embodiments, the resonance frequency can be
identified for each sensor 140 by pulsing each LC circuit at a
sampling rate ranging from, for example 10 to 1000 times per
second, with each pulse causing the LC circuit to oscillate at its
respective resonance frequency (f) (e.g., 1 MHz to 10 MHz). In
other embodiments, the resonance frequency can be identified for
each sensor 140 from a continuous waveform at the resonant
frequency of the LC circuit by re-energizing the LC circuit on each
cycle by injecting electrical energy into the LC circuit at the
correct phase of the waveform.
[0100] FIG. 11 shows circuitry which can support pulsing each
sensor 140 at a sampling rate and then measuring its resonance
frequency. FIG. 11 shows the distal mass 133 having a variable
distance from the inductor 151. Inductor 151 is part of an LC
circuit 150 and electrically parallel with the capacitor 152. A
switch 153 can electrically connect the LC circuit 150 with an
excitation branch 170 or a measurement branch 171. The excitation
branch 170 includes a driver 155 which can generate pulses of
electrical energy as shown in excitation signal 158. The timing of
pulses can be determined in part by clock 156. The switch 153 can
alternatively connect the LC circuit 150 to the measurement branch
171. It is noted that the LC circuit 150 includes a node 154 which
can be used as a reference for making voltage measurements across
the LC circuit 150 together with the measurement branch 171. The
measurement branch 171 includes an amplifier 160 which can output
sinusoidal signal 161 indicative of the oscillation in the LC
circuit 150 due to one excitation pulse from driver 155. A
threshold detector 162 can be used to identify the period of a
cycle of the sinusoidal signal 161 as shown by signal 163. A
digital comparator 165 can identify a preset number of oscillation
cycles from the signal 163. The identification of the cycles can be
facilitated by input from the clock 156 which can indicate, among
other things, the timing of the excitation pulses of the excitation
signal 158. Based on the clock 156 and the timing of the
oscillation cycles, a frequency of oscillation measured from the
measurement branch 171 can be determined for each excitation cycle
output (e.g., corresponding to each pulse) by the excitation branch
170. Thus, for each excitation pulse, a resonance frequency can be
measured. The resonance frequency can be sent from an output 166 to
the processor 127 (FIG. 2) or to a processor within the force
sensing subsystem 126 to compare to recent resonance frequency
values for the same LC circuit 150 to detect a change in frequency
over time (e.g., relative to a baseline indicating no force), which
can be related to a change in force.
[0101] FIG. 12 shows circuitry which can support continuously
oscillating each sensor 140 to produce a continuous sinusoidal
output and then measuring its resonance frequency. Unlike the
pulsed embodiment described above in reference to FIG. 11, this
embodiment does not need the switch 153 in each sensor 140 because
it does not have separate excitation and measurement branches. FIG.
12 shows the distal mass 133 having a variable distance from the
inductor 151. Inductor 151 is part of an LC circuit 150 and
electrically parallel with the capacitor 152. The LC circuit 150
can be electrically connected to an amplifier 160. A positive
feedback device 164 can connect a node 167 at the output of the
amplifier 160 to a node 169 at the input of the amplifier 160 to
re-energize the LC circuit 150 such that the amplifier 160 outputs
sinusoidal signal 172 indicative of the oscillation in the LC
circuit 150. A threshold detector 162 can be used to identify the
period of a cycle of the sinusoidal signal 172 as shown by signal
173. A digital comparator 165 can identify a preset number of
oscillation cycles from the signal 173. The identification of the
cycles can be facilitated by input from the clock 156. Based on the
clock 156 and the timing of the oscillation cycles, a frequency of
oscillation can be determined. The resonance frequency can be sent
from an output 166 to the processor 127 (FIG. 2) or to a processor
within the force sensing subsystem 126 (FIG. 2) to compare to
recent resonance frequency values for the same LC circuit 150 to
detect a change in frequency over time (e.g., relative to a
baseline indicating no force), which can be related to a change in
force.
[0102] The circuits shown in FIGS. 11 and 12 can be duplicated but
without a variable distance mass of high magnetic permeability
material. Such a duplicate circuit may function as a control sensor
to cancel out noise. For example, the control sensor can be located
proximally of the proximal mass 132. Changes in the resonance
frequency of the control sensor can be subtracted from changes in
resonance frequency of the other sensors 140 to cancel out
environmental noise interference or variations due to changes in
temperature.
[0103] As shown in FIG. 6, the sensors 140 are circumferentially
arrayed about the sensor support 134. If the force exerted on the
distal segment 113 of the catheter 110 is coaxial with the
longitudinal axis 109, then each of the sensors 140 will indicate
equal amounts of resonance frequency change (and therefore equal
amount of movement relative to the distal mass 133). Based on these
equal changes, the control circuitry can determine a magnitude and
direction of the force. In some embodiments, the displacement
relative to each sensor 140 can be calculated based on the change
in resonance frequency for that sensor 140 and the change in
dimension can then be used to calculate force based on Hooke's law.
Alternatively, the force can be calculated using a combined
equation that incorporates Hooke's law and the equation for
determining the displacement (x) from the resonance frequency (f)
for an LC circuit (e.g., Equation 2). Returning to the above
example in which the changes in resonance frequency and
displacements are respectively equal for each of the sensors 140,
the control circuitry can determine that the force is coaxial with
the longitudinal axis 109.
[0104] If the force is not coaxial with the longitudinal axis 109,
then distal segment 113 will tend to curl or shift radially away
from the force with respect to the proximal segment 111. In such
cases, the sensors 140 will indicate different changes in resonance
frequency. For example, all sensors 140 may indicate different
levels of decreasing resonance frequency. In some cases, one or
more sensors 140 may indicate an increasing resonance frequency,
while one or more other sensors 140 may indicate a decreasing
resonance frequency. Which sensors 140 indicate increasing
resonance frequency and which sensors indicate decreasing resonance
frequency depends on the direction of the force and the off-axis
movement of the distal segment 113 relative to the proximal segment
111. If the force had a different direction, a different one or
more of the sensors 140 will indicate an increasing resonance
frequency while another will indicate a different level of
resonance frequency change or a decrease in resonance frequency.
Generally, the one or more sensors 140 that indicate a decrease in
resonance frequency indicate the direction from which the force is
coming while the one or more sensors 140 that indicate an increase
in resonance frequency indicate the opposite direction (in which
the force is pointed or going). Based on this, the direction (e.g.,
unit vector) of the force can be determined by the control
circuitry. It is noted that baseline resonance frequency values can
be determined for each of the sensors 140 based on a number of
consecutive constant resonance frequency values. Deviation from
this baseline indicates a force acting on the catheter.
[0105] Once assembled, the catheter 110 may undergo a calibration
step, either at a factory or just before use by a physician. In
such a step, a plurality of forces of known magnitude and direction
can be placed, in sequence, on the distal segment 113 to move the
distal segment 113 relative to the proximal segment 111, while the
sensors 140 output signals or otherwise exhibit changes in
resonance frequency indicative of the strain of the spring element
135. A table can be generated indicating a separate entry for each
calibration force value (magnitude and direction). Thereafter, a
force of unknown magnitude and/or direction can be analyzed by
comparing signals output from the sensors 140 to the values of the
table to identify the best match. An algorithm can identify which
entry from the calibration data has three (or other number
depending on the number of sensors 140) change-in-resonance
frequency values best matching the current change-in-resonance
frequency values. The magnitude and direction of the known force
from the calibration step can be indicated as the magnitude and
direction currently being experienced. In some cases, a
mathematical relationship can be generated based on the linearity
of Hooke's law, wherein a limited number of calibration steps are
performed to determine the change-in-resonance frequency, or other
parameter, and interpolation and/or extrapolation can be computed
based on these calibration values. For example, the spring constant
can be determined for the spring element 135 such that a subsequent
amount of change in separation distance between a sensor 140 and
the distal mass 133 can be multiplied by the spring constant to
determine the magnitude of the force acting on the distal segment
113. The changes in separation distance for multiple sensors 140
can be factored for determining an overall magnitude and direction
for the force.
[0106] The magnitude can be represented in grams or another measure
of force. The magnitude can be presented as a running line graph
that moves over time to show new and recent force values. The
direction can be represented as a unit vector in a three
dimensional reference frame (e.g., relative to an X, Y, and Z axes
coordinate system). In some embodiments, a three dimensional
mapping function can be used to track the three dimensional
position of the distal end 116 of the catheter 110 in the three
dimensional reference frame. Magnetic fields can be created outside
of the patient and sensed by a sensor that is sensitive to magnetic
fields within distal end 116 of the catheter 110 to determine the
three dimensional position of the distal end 116 of the catheter
110 in the three dimensional reference frame. The direction can be
represented relative to the distal end 116 of the catheter 110. For
example, a line projecting to, or from, the distal segment 113 can
represent the direction of the force relative to the distal segment
113. Such representations can be made on a display as discussed
herein.
[0107] In some embodiments, the magnitude and direction of the
force that are indicated to the user indicate the magnitude and the
direction of a force that acts on the distal segment 113. This
force typically results from the distal segment 113 pushing against
tissue. Therefore, the force acting on the distal segment 113 may
be a normal force resulting from the force that the distal segment
113 exerts on the tissue. In some embodiments, it is the force
acting on the distal segment 113 that is calculated and represented
to a user. Additionally or alternatively, it is the force that the
distal segment 113 applies to the tissue that is calculated and
represented to the user.
[0108] The magnitude and direction of the force can be used for
navigation by providing an indicator when the catheter encounters
tissue and/or for assessing the lesioning of tissue by determining
the degree of contact between the lesioning element and the tissue,
among other options. In some embodiments, a force under 10 grams is
suboptimal for lesioning tissue (e.g., by being too small) while a
force over 40 grams is likewise suboptimal for lesioning tissue
(e.g., by being too large). Therefore, a window between 10 and 40
grams may be ideal for lesioning tissue and the output of the force
during lesioning may provide feedback to the user to allow the user
to stay within this window. Of course, other force ranges that are
ideal for lesioning may be used.
[0109] The techniques described in this disclosure, including those
attributed to a system, control unit, control circuitry, processor,
or various constituent components, may be implemented wholly or at
least in part, in hardware, software, firmware or any combination
thereof. A processor, as used herein, refers to any number and/or
combination of a microprocessor, a digital signal processor (DSP),
an application specific integrated circuit (ASIC), a
field-programmable gate array (FPGA), microcontroller, discrete
logic circuitry, processing chip, gate arrays, and/or any other
equivalent integrated or discrete logic circuitry. As part of the
control circuitry, at least one of the foregoing logic circuitry
can be used, alone or in combination with other circuitry, such as
memory or other physical medium for storing instructions, can be
used to carry about specified functions (e.g., a processor and
memory having stored program instructions executable by the
processor for determining a magnitude and a direction of a force
exerted on a catheter based on a change in resonance of at least
one sensor circuit within the catheter). The functions referenced
herein may be embodied as firmware, hardware, software or any
combination thereof as part of control circuitry specifically
configured (e.g., with programming) to carry out those functions,
such as a means for performing the functions referenced herein. The
steps described herein may be performed by a single processing
component or multiple processing components, the latter of which
may be distributed among different coordinating devices. In this
way, control circuitry may be distributed between multiple devices.
In addition, any of the described units, modules, subsystems, or
components may be implemented together or separately as discrete
but interoperable logic devices of control circuitry. Depiction of
different features as modules, subsystems, or units is intended to
highlight different functional aspects and does not necessarily
imply that such modules or units must be realized as hardware or
software components and/or by a single device. Rather, specified
functionality associated with one or more module, subsystem, or
unit, as part of a control circuitry, may be performed by separate
hardware or software components, or integrated within common or
separate hardware or software components of control circuitry.
[0110] When implemented in software, the functionality ascribed to
the systems, devices, and control circuitry described in this
disclosure may be embodied as instructions on a physically embodied
computer-readable medium such as RAM, ROM, NVRAM, EEPROM, FLASH
memory, magnetic data storage media, optical data storage media, or
the like, the medium being physically embodied in that it is not a
carrier wave, as part of control circuitry. The instructions may be
executed to support one or more aspects of the functionality
described in this disclosure.
[0111] Various modifications and additions can be made to the
exemplary embodiments discussed without departing from the scope of
the present invention. For example, while the embodiments described
above refer to particular features, the scope of this invention
also includes embodiments having different combinations of features
and embodiments that do not include all of the described features.
Accordingly, the scope of the present invention is intended to
embrace all such alternatives, modifications, and variations as
falling within the scope of the claims, together with all
equivalents thereof.
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